Method and instrumentation for posterior interbody fusion

ABSTRACT

A method and instrumentation for spinal interbody fusion is disclosed. The instruments and methods are particularly adapted for interbody fusion from a posterior approach to the spine. One instrument is a retractor having a lockable pivotally mounted handle. Another instrument is a template for straddling the dura. A modular distractor is also provided and preferably includes a tapered shaft with a visualization window disposed therein. Yet another instrument is a depth gauge to verify bone opening depth and dimension, preferably including a radiopaque portion. A method contemplates the use of these instruments to prepare a disc space to receive an implant.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to surgical proceduresfor spinal stabilization and more specifically to instrumentation andtechniques for inserting a spinal implant within the intervertebral discspace between adjacent vertebra. More particularly, while aspects of thepresent invention may have other applications, the invention providesinstruments and techniques especially suited for interbody fusion from agenerally posterior approach to the spine

[0002] Various surgical methods have been devised for the implantationof fusion devices into the disc space. Both anterior and posteriorsurgical approaches have been used for interbody fusions. In 1956, RalphCloward developed a method and instrumentation for anterior spinalinterbody fusion of the cervical spine. Cloward surgically removed thedisc material and placed a tubular drill guide with a large foot plateand prongs over an alignment rod and then embedded the prongs intoadjacent vertebrae. The drill guide served to maintain the alignment ofthe vertebrae and facilitated the reaming out of bone material adjacentthe disc space. The reaming process created a bore to accommodate a bonedowel implant. The drill guide was thereafter removed following thereaming process to allow for the passage of the bone dowel which had anouter diameter significantly larger than the reamed bore and the innerdiameter of the drill guide. The removal of the drill guide left thedowel insertion phase completely unprotected. Thus, Cloward's method andinstrumentation was designed for and limited to an anterior surgicalapproach and was inappropriate for a posterior application.

[0003] Furthermore, B. R. Wilterberger described in a paper entitled“Dowel Intervertebral Fusion as Used in Lumbar Disc Surgery” (publishedin The Journal of Bone and Joint Surgery, volume 39A, pgs. 234-92,1957), the unprotected drilling of a hole from a posterior approach intothe lumbar spine between the nerve roots and across the disc space, andthen inserting a bone dowel into that disc space. While Wilterberger hadtaken the Cloward concept of circular drilling followed by dowel fusionand applied it to the lumbar spine from a posterior approach, he had notfurther improved the method, nor had he advanced the instrumentation toprovide adequate protection for the sensitive vessels and neurologicalstructures adjacent to the operating field.

[0004] U.S. Pat. No. 5,484,437 to Michelson discloses a technique andassociated instrumentation for inserting a fusion device from aposterior surgical approach that provides greater protection for thesurrounding tissues and neurological structures during the procedure. Asdescribed in more detail in the '437 patent, the surgical techniqueinvolves the use of a distractor having a penetrating portion that urgesthe vertebral bodies apart to facilitate the introduction of thenecessary surgical instrumentation. The '437 patent also discloses ahollow sleeve having teeth at one end that are driven into the vertebraeadjacent the disc space created by the distractor. These teeth engagethe vertebra to maintain the disc space height during subsequent stepsof the procedure following removal of the distractor. In accordance withone aspect of the '437 patent, a drill is passed through the hollowsleeve to remove portions of the disc material and vertebral bone toproduce a prepared bore for insertion of the fusion device. The drill isthen removed from the sleeve and the fusion device is positioned withinthe disc space using an insertion tool.

[0005] While the more recent techniques and instrumentation represent anadvance over earlier surgical procedures for the preparation of the discspace and insertion of the fusion device, the need for improvement stillremains. The present invention is directed to this need and providesconvenient methods and instruments to insure safe and effectivepreparation of a disc space in conjunction with implant placement.

SUMMARY OF THE INVENTION

[0006] One object of the present invention is to provide an improvedretractor assembly permitting variable placement of the handle withrespect to a retractor blade. The retractor comprises a retractor blade,a shaft having a first portion connected to the retractor blade, and anopposite second portion pivotally connected to a handle. Preferably, theassembly further includes a locking mechanism selectively locking thehandle to the second portion to limit pivotal movement of the handle inrelation to the shaft.

[0007] In another aspect of the present invention, a method of duraretraction is provided for posterior access to the spine. The methodcomprises providing a retractor having a retractor blade pivotallyconnected to a handle, and the handle having a locking mechanism toselectively lock the handle to the retractor. A portion of the dura isexposed and the retractor is inserted with the handle in an insertionposition and the locking mechanism in a locked position. The dura isthen retracted to expose underlying spinal elements. Preferably, thelocking mechanism is unlocked to allow the handle to pivot in relationto the retractor blade. In this aspect, the handle is pivoted to aholding position and locked to maintain the handle in the lockedposition.

[0008] Yet a further aspect of the present invention is a template forstraddling the dura in a spinal surgery to facilitate marking a surgicalsite to gain access to the disc space in preparation for implantplacement. The template comprises a body having an upper surface and alower surface facing the dura, and an opening formed between the uppersurface and the lower surface. A shaft having a first end and a secondend is connected to the body and extends away from the upper surface.Preferably, a working tube is connected to the body in substantialalignment with the opening and extends from the lower surface, the tubehaving a first diameter. A locator extension engages the body and isspaced from the tube to provide a space for passage of the duratherebetween. The locator extension extends from the lower surface andhas a second diameter that is less than the tube diameter. Optionally,the body may be formed to match the maximum area of the insertioninstrumentation at the engagement with the vertebral bodies, therebyallowing marking of the bone needing removal.

[0009] Still a further object of the present invention is to provide aspinal disc space distractor assembly. Preferably, the distractorincludes a tapered shaft portion. Optionally, a window may be formedthrough the shaft for visualization. In one form of the invention, theassembly comprises a driving portion removably coupled to a distractortip. The driving portion is coupled to transmit rotational andlongitudinal forces. Preferably the assembly includes an outer shafthaving a first driving shoulder for transmitting rotational force endand an opposite second driving shoulder for receiving a rotationalforce. An inner shaft is slidably disposed within at least a portion ofthe outer shaft, the inner shaft having a first connection end and anopposite second connection end. The first connection end is disposedadjacent the first driving shoulder. The assembly further includes adistraction tip, the tip having a driving surface adapted for engagementwith the first driving shoulder and a connection surface adapted forengagement with the first connection end. A handle interconnects theinner and outer shafts and maintains the tip in contact with the outershaft. In one embodiment the outer shaft is tapered to provide greatervisualization. Further, the outer shaft may have a visualization windowextending there through.

[0010] It is yet a further object to provide an instrument fordetermining the depth and size of an opening formed between two adjacentvertebral bodies. The instrument comprises an elongated shaft andpreferably a radiolucent tip attached to the shaft, the tip including atleast on radiopaque marker. Preferably, the instrument includes a distaltip sized to match the diameter or shape of the opening intending to becreated.

[0011] The present invention also contemplates a method of preparing adisc space and inserting an implant. The method utilizes one or more ofthe instruments described above to prepare the disc space for receivingan implant.

[0012] Related objects and advantages of the present invention will beapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1(a) is a perspective view of a retractor according to thepresent invention.

[0014]FIG. 1(b) is a partial cross-sectional side view of the retractorof FIG. 1.

[0015]FIG. 2(a) is an end view of a shaft of a portion of the retractorof FIG. 1.

[0016]FIG. 2(b) is a side view of the retractor shaft of FIG. 1.

[0017]FIG. 3(a) is a side view of the handle of FIG. 1.

[0018]FIG. 3(b) is a bottom view of the handle of FIG. 3(a).

[0019]FIG. 4(a) is a perspective view of an intraoperative templateaccording to another aspect of the present invention.

[0020]FIG. 4(b) is a partial cross-sectional side view of theintraoperative template of FIG. 4(a).

[0021]FIG. 5 is a perspective view of a further embodiment of anintraoperative template according to the present invention.

[0022]FIG. 6 is a perspective view of still a further embodiment of anintraoperative template according to the present invention.

[0023]FIG. 7 is perspective view of the intraoperative template of FIG.6 with handle and trephine.

[0024]FIG. 8 is a perspective view of yet a further embodiment of anintraoperative template according to the present invention.

[0025]FIG. 9 is a perspective view of still a further intraoperativetemplate.

[0026]FIG. 10 is a cross-sectional view of the embodiment of FIG. 4(a).

[0027]FIG. 11 is a perspective view of a distractor according to thepresent invention.

[0028]FIG. 12(a) is an exploded perspective view of a modular distractoraccording to the present invention.

[0029]FIG. 12(b) is a substantially assembled perspective view of themodular distractor of FIG. 12(a).

[0030]FIG. 13 is a plan elevation of a fully assembled distractor ofFIG. 12(b).

[0031] FIGS. 14(a) through 14(c) are partial cross-sectional side viewstaken along line 14 a-14 a showing the modular distractor according toFIG. 13.

[0032]FIG. 15 is a side elevational view of an outer sleeve according tothe present invention.

[0033]FIG. 16 is a side view of the outer sleeve of FIG. 15 rotated 90°about the longitudinal axis.

[0034]FIG. 17 is a perspective view of the outer sleeve of FIG. 15 incombination with the distractor of FIG. 13.

[0035]FIG. 18 is a perspective view of a depth stop according to oneaspect of the present invention.

[0036]FIG. 19(a) is a side-elevational view of the depth stop of FIG.22.

[0037]FIG. 19(b) is a side view of the depth stop of FIG. 19(a) rotated90° about its longitudinal axis.

[0038]FIG. 19(c) is a cross-sectional view of the depth stop of FIG.19(b).

[0039]FIG. 20 is a side-elevational view of an alternative embodiment ofa depth stop according to the present invention.

[0040]FIG. 21 is a perspective view of an outer sleeve in combinationwith a depth stop and reamer.

[0041]FIG. 22 is a perspective view of a depth gauge according to oneaspect of the present invention.

[0042]FIG. 23 is a perspective view of the depth gauge of FIG. 22 incombination with an outer sleeve.

[0043]FIG. 24 is a perspective view of a tap in combination with anouter sleeve.

[0044]FIG. 25 is a perspective view of an implant inserter in accordancewith another aspect of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated devices, and such furtherapplications of the principles of the invention as illustrated thereinbeing contemplated as would normally occur to one skilled in the art towhich the invention relates.

[0046] The present invention relates generally to instruments andmethods for performing vertebral interbody fusion. While it should beunderstood that the instruments disclosed herein may have many uses, itis particularly contemplated that they may be used to perform vertebralinterbody fusion from a generally posterior approach to the spine. Suchprocedures typically involve the placement of dowels or other implantsinto the intervertebral disc space to promote fusion between adjacentvertebral bodies and to stabilization of the spine. Such implants may beformed of metal, ceramics, composites, bone or other bio-compatiblematerials, depending on the properties desired from the implant.

[0047] Referring now to FIG. 1(a), there is shown a retractor mechanismaccording to one aspect of the present invention. Retractor 10 includesa handle 12 pivotally connected to a shaft 14 having a distal end 17connected to a retractor blade 16. While retractor blade 16 is shown asa semi-circular blade, it is contemplated that any of a variety ofretractor blade shapes may be utilized in conjunction with handle 12 andshaft 14 of the present invention. Handle 12 is pivotable in relation toshaft 14 and may be releasably connected to shaft 14 adjacent enlargedend 18. As shown more clearly in FIG. 2, enlarged end 18 includes aseries of grooves 24 on its upper surface 36. Handle 12 includes alocking mechanism 22 adapted to selectively engage annular groove 26extending around enlarged end 18 of shaft 14, and at least one ofgrooves 24 disposed on the upper surface 36.

[0048] Referring specifically to FIG. 1(b), locking mechanism 22includes a flange 28 adapted for engaging a portion of annular groove 26disposed on shaft 14. As shown in FIG. 3(b), flange 28 extends in asemi-circular fashion and includes substantially parallel straightextensions 31 and 33 positioned adjacent opening 35. Flange 28 definesan opening 35 for receiving a portion of the enlarged head 18 of shaft14 to hold the shaft and handle in mating engagement. Locking mechanism22 further includes an upper plate 34 having a downwardly extendinginternal projection 30 adapted to engage one of grooves 24 on shaft 14.Although only a single projection 30 is shown, it will be understoodthat multiple projections may be provided to engage one or more grooveson shaft 14. Disposed within handle 12 is an inner shaft 23 slidablewithin outer shaft 32 to at least partially close opening 35 to preventpassage of enlarged end 18 from the channel formed by flange 28. Theposition of inner shaft 23 is controlled by movement of thumb lever 20sliding within slot 21 formed in outer shaft 32. Inner shaft 23 includesa projection 29 adapted to engage a portion of annular groove 26.Preferably, inner shaft 23 is biased to an extended position shown inFIG. 1(b) by spring 38 captured within outer shaft 32. In the extendedposition, inner shaft 23 retains handle 12 and shaft 14 in lockedengagement.

[0049] In a locked position, flange 28 of locking mechanism 22 engages asemi-circular portion of annular groove 26 and projection 29 on innershaft 23 also engages a further portion of annular groove 26. Thisengagement maintains handle 12 and shaft 14 securely engaged. To inhibitpivotal movement in the locked position, grooves 24 on enlarged end 18are urged into engagement with projection 30 of locking mechanism 22,thereby positioning the projection in one of the grooves 24 to preventrotation of handle 12 about the longitudinal axis of shaft 14. In anadjustment position, projection 29 may be partially withdrawn fromannular groove 26 by movement of thumb lever 20 in the direction ofarrow 25. With projection 29 in the adjustment position, there may besufficient transverse movement of shaft 14 within opening 35 todisengage projection 30 from grooves 24 thereby permitting pivotalmovement of handle 12 in relation to shaft 14 without complete removalof the handle. In the adjustment position, inner shaft 23 preventsmovement of shaft 14 entirely out of opening 35, thus maintaining theconnection between handle 12 and shaft 14. With the locking mechanism inthe adjustment position, the handle may be pivotally repositioned to avariety of positions. It will be understood that in a preferredembodiment, shaft 14 includes eight grooves 24, thereby permittinghandle 12 to be locked in eight separate pivotal positions about shaft14. Although eight grooves 24 are shown, it is contemplated that more orless grooves may be provided to accommodate various positions. Moreover,while grooves are shown on the top of shaft 14, it is contemplated thatthese may be placed around the exterior of enlarged head 18 to engage aprojection correspondingly disposed in locking mechanism 22. Further,the placement of grooves and projections may be reversed such that theshaft includes one or more projections mating with grooves in thelocking mechanism. Other mechanisms known to those skilled in the artfor allowing selective pivotal movement between the shaft and handle arecontemplated and come within the scope of the present invention.

[0050] In an unlocked position, projection 29 of inner shaft 23 iscompletely withdrawn from opening 35 by further movement of thumb lever20 in the direction of arrow 25, thereby allowing enlarged end 18 to beremoved from locking mechanism 22. The locking mechanism may also beplaced in the unlocked position to insert a tool shaft.

[0051] Utilization of the above-described retractor device providesseveral advantages over retractors utilizing a fixed handle position.Specifically, in a first locked handle position, a surgeon may positionthe retractor device 10 to most effectively retract a desired neuralstructure or vessel. Once the surgeon has properly positioned theretractor adjacent the desired tissue and the tissue is retracted,handle locking mechanism 22 may be moved to the adjustment position andhandle 12 pivoted about shaft 14 to a position for an assistant tomaintain the tissue or vessel in the retracted position. Often, theassistant will be located on the opposite side of the patient from thesurgeon and it is desirable that the handle be rotated out of thesurgical field to provide the best access and visualization of thesurgical site for the surgeon. Once properly positioned, the lockingmechanism may be returned to the locked position to securely hold thehandle and shaft in the selected arrangement. Further, handle 12 may beremoved from shaft 14 and utilized with a variety of instruments, suchas those disclosed further herein. Use of a removable handle having theadvantages described above may limit the total number of handlesrequired for a surgical procedure or that must be supplied with asurgical set.

[0052] Referring now to FIGS. 4(a) and (b), there is shown anintraoperative template 40 according to another aspect of the presentinvention. Template 40 includes a shaft 42 interconnected with handle44. Shaft 42 is centrally connected to the upper side of template body48. Template body 48 defines a number of bone marking notches 50 aroundits perimeter and includes an integrally formed guide tube 46 extendingfrom its lower surface. Although an integrally formed guide tube isshown in a preferred embodiment, it will be understood that a removableguide tube may be connected adjacent an aperture in the body. Guide tube46 defines a channel 47 to receive an instrument. Body 50 furtherdefines an opening 49 adapted to receive a locator extension 51.

[0053] In FIG. 4(b) there is shown a partial cross-sectional view of thetemplate of FIG. 4(a). Inserted within opening 49 is a removable locatorextension 51 having a head 53. In a preferred embodiment locatorextension 51 may be threadably received with opening 49 to preventdislodgment. Diameter 41 of guide tube 46 is substantially larger thandiameter 43 of locator extension 51. The additional space created byutilization of a locator extension rather than a second guide tube sizedto receive a cutting instrument limits the amount of compression thatthe dura 45 must undergo and increases the possibility that such atemplate may be utilized. Preferably, guide tube 46 and locatorextension 51 are in substantially parallel alignment.

[0054] Referring now to FIG. 5, there is disclosed a second embodimentof an intraoperative template according to the present invention. Asecond template 52 includes a handle 54 connected to a shaft 56 which iscentrally connected to template body 58. Template body 58 furtherincludes guide tube 60 and integrally formed post 62. A trephine 64 isillustrated extending into and through guide tube 60 with trephinecutting head 66 extending beyond distal end 61 of guide tube 60. Theaddition of post 62 to the template permits a surgeon to straddle thedura and place post 62 to further assist in the alignment of any furthertrephining procedures.

[0055] Referring now to FIG. 10, template body 48 includes sixindentations 50 along the perimeter of the device. The perimeter of thedevice matches the amount of exposure required for placement of a pairof implants. Preferably, the body is sized to match the space needed toplace two cylindrical bone dowels. Therefore, if in placing templatebody 48, bony structures are encountered which extend into the areaneeded for implant placement, notches 68, 70, 72, and similar notches onthe other portion of the template permit marking of the interferingstructure and ultimately passage of a working channel for placement ofinterbody fusion devices.

[0056]FIGS. 6 and 7 illustrate still a further embodiment of anintraoperative template according to the present invention.Intraoperative template 80 includes a shaft 82 and an enlarged end 84similar to the enlarged end 18 previously described on shaft 14 of theretractor mechanism disclosed in FIG. 1. As such, handle 98 is identicalto handle 12 and may be pivotally positioned on shaft 82. Intraoperativetemplate 80 includes a template body 86, a guiding tube 88, and anaperture 94 extending through template body 86. As shown in FIG. 6, aremovable post 92 with attached handle 90 has been placed in opening 94to drop into a first trephine hole or to penetrate the disc annulus tostabilize the template during trephining of a first hole through guidetube 88. It will be understood that post 92 and handle 90 may be removedfor unilateral templating if desired.

[0057] Referring now to FIG. 7, there is shown the intraoperativetemplate of FIG. 6 with interconnected handle 98 joined by connectionmechanism 100 as previously described with respect to the retractormechanism of FIG. 1. A trephine 96 is further disclosed extendingthrough guide tube 88.

[0058] In FIG. 8 there is illustrated a further embodiment of a templateaccording to the present invention. Template 116 has a template body andguide tube as previously described with respect to FIG. 6. In thisembodiment, shaft 117 includes an offset portion 118 laterallyoffsetting enlarged head 119 from the lower portion of the shaft. Itwill be understood that this limits the amount of instrumentation withinthe surgical field and permits greater access.

[0059] Referring now to FIG. 9, there is shown yet a further embodimentof an intraoperative template according to another aspect of the presentinvention. Intraoperative template 101 includes a connection mechanism104 on shaft 102, a template body 106, guiding tube 108, and a post 110.In contrast to the previous embodiments, post 110 includes asubstantially straight portion 112 in substantial alignment with theconnection 113 of post 110 to template body 106. Between straightsection 112 and connection 113, is a laterally extending curved portion114. It will be understood that the curvature of rod 112 away from tube108 provides still further space for disposing the dura 116 between tube108 and post 110 during the templating procedure. Post 110 may beremovably secured to body 106. Moreover, post 110 is illustrated havinga particular curve, it being understood that the locator extension maytake an alternative configuration and remain within the scope of thepresent invention.

[0060] Referring now to FIG. 11, there is shown a distractor accordingto another aspect of the present invention. Distractor 130 includes ashaft 131 with a Hudson-type connection 132 and markings 134 indicatingthe distraction height created in the disc space by the distraction tip136. Disposed adjacent indicators 134 is a substantially uniformdiameter guiding portion 144. Extending further towards distraction tip136 is a continuously tapering portion 142. Disposed adjacent distractortip 136 is a further set of indicators 138, again indicating the heightof distraction in the disc space created by the orientation of tip 136.Disposed within tapering section 142 is a visualization window 140extending entirely through shaft 131 permitting visualization ofstructures and vessels on the opposite side of the shaft. The distractortip of FIG. 11 is a two-position distractor having an insertion positionwith a first working distraction height. If the first workingdistraction height is insufficient or a greater distraction is desired,the shaft may be rotated 90° to a second greater working distractionheight.

[0061] Referring to FIGS. 12 through 14, there is disclosed a modulardistraction assembly 150 permitting interchangeability of distractiontips, as well as the ability to leave the distraction tip disposedwithin the disc space while removing the insertion tool. Referring morespecifically to FIG. 12(a), the modular distraction assembly 150includes a T-handle 180 with a conventional Hudson-type connectionmechanism 181 disposed therein. The assembly further includes an innershaft 152 having an enlarged end 154 adapted for engagement with Hudsonmechanism 181 and an opposite threaded end 156. Inner shaft 152 may bedisposed within outer tube 160. Outer tube 160 includes a slot driver162 and an opposite end driving extension 164 having flats 166 forengagement with the T-handle 180 to transmit rotational force to outertube 160. Preferably, outer tube includes a visualization window 168extending therethrough. Distractor tip 176 has an internal channel 179defining internal threads 177 for engagement with threaded end 156 ofinner shaft 152 and a slot 178 for engagement with the slot driver ofouter tube 160 (see FIG. 14(c)).

[0062] Referring now to FIGS. 14(a) through (c), there is shown across-section of the assembled modular distraction assembly 150. Asshown in FIG. 14(b), enlarged end 155 of inner shaft 152 is advancedpast balls 186 such that the balls are adjacent a smaller outer diameter157 of the inner shaft 152. Collar 184 is then advanced towards outertube 160 such that inclined surfaces 188 extend below balls 186 andreduced internal diameter portion 190 is disposed adjacent balls 186 toforcibly urge balls 186 against reduced outer diameter 157 of shaft 152.It will be understood that the engagement of balls with inner shaft 152securely holds the inner shaft in position. Handle 180 includes a shaftportion 181 having a configuration adapted to engage the driving flatsof extension 164. It will be understood that with collar 184substantially advanced towards shoulder 165, the inner shaft and outertube are substantially engaged with handle 180. To complete theengagement in a preferred embodiment, inner shaft 152 must be threadedlyengaged with distraction tip 176 prior to attachment of T-handle suchthat the distal end 171 of outer tube 160 engages the enlarged head 173of distraction tip 176 to secure the outer tube 160 in engagement withhandle 180. It will be understood that to disengage the assembly, collar184 must be pulled toward handle 180 until balls 186 are adjacentinclined surfaces 188 and allowed to move away from inner shaft 152. Inthis position, handle 180 may be displaced longitudinally away fromouter tube 160 and removed. Once handle 180 has been removed, innershaft 152 may be rotated to threadedly disengage from distractor tip176, thereby allowing the inner shaft and outer tube 160 to bedisengaged from distractor tip 176. Inner shaft 152 is preferablyretained within outer tube 160 by threads 161. Threads 161 are largerthan the internal diameter of threaded opening 163. For completeremoval, threads 161 may be threadedly passed through threaded opening163.

[0063] Referring now to FIGS. 15 and 16, there is shown an outer sleevein accordance with another aspect of the present invention. Outer sleeve210 includes a distractor portion 212 having a tip 216 and taperingportion 214 extending back to an area of grooves 218 adapted to engageadjacent bony structures. An opposing distractor portion 213 issimilarly formed. The bone engaging portion further includes spikes 220and 221 adapted to be driven into bony structures adjacent the discspace. Outer sleeve 210 further includes visualization windows 222 and224. Window 222 extends to extended side wall 226. In contrast, window224 extends closer to the engagement end and terminates adjacent sidewall 228. It can be seen that side wall 226 is substantially longer thanside wall 228 along longitudinal axis 211. As shown in FIG. 15, thelonger portion of side wall 226 is provided to engage and protect nerveroots exiting the spinal cord adjacent the surgical site. In contrast,shortened wall 28 provides greater visualization through window 224.Additionally, outer tube 210 includes a markings visualization window232 for visualizing markings on instruments in the tube indicating thedepth of instrument penetration into the disc space.

[0064] Referring now to FIG. 17, there is shown a combination of thedistractor assembly 150 having a distractor tip 176 in combination withouter sleeve 210. Window 224 permits visualization of the distractorassembly while window 232 permits visualization of markings along thedistractor assembly shaft indicating the depth of penetration of thedistractor and/or outer sleeve. It will be understood that in a typicalprocedure, distraction assembly 150 is placed prior to the insertion andplacement of outer sleeve 210.

[0065] Referring now to FIGS. 18 through 20, there is disclosed a depthstop mechanism preferably cooperable with the shaft of a tool and anouter sleeve as disclosed herein. Such tools can include, withoutlimitation, the reamer and the tap. Depth stop 300 includes an enlargedcircumferential abutment shoulder 310 adapted to engage the proximal endof an outer working sleeve to prevent further advancement of the stopand any interconnected shaft. Stop 300 further includes viewing windows308 to permit visualization of depth markings on a shaft extendingwithin the stop. Stop 300 includes a manually operated collar 302 whichmay be axially displaced along axis 301 in the direction of arrow 305 toallow flexing of fingers 306. Collar 302 is normally urged into anextended position by spring 316. Referring specifically to FIG. 19(c),fingers 306 include projections 304 extending internally. The internalprojections 304 are configured for engagement within grooves definedalong a tool shaft of a working tool. Additionally, each finger includesan external taper portion 312 adapted for engagement with bearingsurface 314 of collar 302. It will be understood that with collar 302 ina retracted position, bearing surface 314 of collar 302 will besubstantially disengaged from taper 312 and thereby permits fingers 306to disengage from the groove of a tool shaft. With collar 302 in theextended position shown in FIG. 19(c), bearing surfaces 314 bear againstthe tapered surface 312 of each finger to urge projections 304 into agroove of a tool shaft. In this manner, a user may quickly and easilydisengage the locking mechanism of the stop to advance or retract a toolshaft and then re-engage the stop at the desired position. However,engagement with the tool shaft is indexed by the spacing of grooves onthe shaft so the exact location of the stop may be easily known. Thetool shaft may be rotated with respect to the stop mechanism to displaythe appropriate depth numeral indicated on the shaft in window 308.Preferably, collar 302 will extend at least partially beyond fingers 306to limit the possibility that surgical staff may snag protective apparelon exposed fingers 306.

[0066] In a first embodiment shown in FIG. 19(a), collar 302 is retainedon housing 306 by retaining pin 322 extending into the housing andthrough a slot 320. Retaining pin 322 prevents rotation of collar 232with respect to housing 318. In an alternate embodiment shown in FIG.24, collar 302 defines an L-shaped slot 324 which permits axialdisplacement of collar 302 with respect to body 318, as well as a slightamount of rotation within the slot. It will be understood that theL-shaped slot 324 permits the depth stop mechanism to be locked in adisengaged position which permits free movement of a tool shaft throughthe depth stop. This is a desirable construction in some instances foreasy removal of the depth stop from the tool shaft, as well as forutilization of the tool without the constraints of a depth stopmechanism.

[0067] Referring now to FIG. 21, there is shown an outer sleeve 210 incombination with a depth stop 300 and reamer 351. The reamer 351 isinterconnected with a T-handle 180 having Hudson connection engaged withthe reamer shaft. It will be understood that depth stop 300 has beenpositioned to engage the upper portion of outer sleeve 210 to preventfurther advancement of the reamer beyond the set depth.

[0068] Referring now to FIG. 22, there is shown a depth gauge accordingto a further aspect of the present invention. Depth gauge 360 includesan upper portion 362 having a plurality of markings 366 indicating thedepth of the distal portion of the gauge into the vertebral bodies.Lower portion 364 is sized to substantially match the outer diameter ofa cylindrical dowel to be inserted into an opening formed betweenadjacent vertebra. It will be understood that close matching of theouter diameter of depth gauge 360 with the desired diameter of the dowelto be placed, will insure that the opening formed between the vertebralbodies in the disc space is substantially clear of debris and closelymatches the outer diameter of the dowel to be placed. Previously, therehas been a possibility that debris could block a portion of the openingdespite the fact that a depth gauge of a smaller diameter may reach thefarthest reaches of the opening. In such a situation, advancement of adowel, particularly in the case of a more brittle bone dowel, may beimpeded by the debris left in the opening, resulting in the possibilityof damage to the dowel and/or the opening when excessive force isapplied to advance the dowel. In a further aspect of the presentinvention, portion 364 is radiolucent and includes a number of markersto identify the location of the depth gauge by radiographic means.Radiomarker 372 indicates the most distal position of the depth gaugeand subsequent position of the implant. Radiographic markings 370 and376 indicate the proximal ends of various sizes of implants. Thedistance 378 between 372 and 370 is approximately 20 mm, a conventionalimplant size, while the distance between 372 and line 376 isapproximately 26 mm, a further conventional implant length.

[0069] Referring now to FIG. 23, there is shown the depth gauge of FIG.22 inserted into and extending beyond outer sleeve 210. The depth ofextension beyond outer sleeve 210 of depth gauge 360 is shown by thenumeral in window 232 in the outer sleeve.

[0070]FIG. 24 illustrates a tap 390 interconnected with the shaft andhandle 180 extending through outer sleeve 210. It will be understoodthat markings on the shaft of the tap may be displayed in window 232 toindicate the length of extension beyond the outer tube. Additionally,the assembly includes an adjustable depth stop 300 which engages theproximal portion of outer sleeve 210 to prevent over-advancement of taphead 390 into the disc space.

[0071] Referring now to FIG. 25, there is shown an implant insertiondevice 400 according to the present invention. The implant insertiondevice includes depth markings along the shaft of the device. Depthmarkings 406 indicate when the dowel is first engaged in the disc space.In the past, it was possible that when one relied only upon feel, thedowel could engage obstructions within the working channel of the outersleeve or other type of inserting device, giving the false impressionthat the implant 402 was engaging the disc space and potentially leadingto damage to the implant as it was forced against the obstruction. Withthe markings 406, multiple markings for different implant lengths, theuser can visually verify whether the implant has engaged the disc space.Markings 404 are provided to indicate the depth the implant has beeninserted into the disc space.

[0072] In use, an initial incision provides the approach and exposure ofthe posterior spinal surgical site. Exposure of the dura is accomplishedin a customary fashion. In one aspect of the method according to thepresent invention, a retractor according to the present invention isused to retract the dura. Once retracted, the pivotal handle of theretractor is pivoted out of the way to permit an assistant to hold theretractor without interfering in the operating field.

[0073] A template in accordance with the present invention may then beplaced to extend on both sides of the dura simultaneously with a guidetube positioned on one side and a locator extension positioned on theopposite side. A trephine is then passed through the guide tube and intothe disc space to remove a portion of the disc and adjacent tissue. Thetemplate may be removed and repositioned to again straddle the dura withthe locator extension in the previously trephined hole and the guidepositioned on the opposite side of the dura. Again, the trephine ispassed through the guide tube and into the disc space to form an openingtherein. With the template remaining in position across the dura, thesurrounding bone structures are evaluated for removal to permitplacement of a guide sleeve. If bone elements, facet or lamina, arepositioned beneath the template body, a marking device such as acautherizer is used to mark the offending structure in one of thenotches provided. After the bone structures have been marked, thetemplate is removed and the bone removed in a conventional manner.Preferably, the template is repositioned to straddle the dura and thefield is again checked to verify that a guide tube may be placed withoutobstruction. If not, further bone marking and removal is conducted. Oncethe space is prepared for guide tube placement, the template is removed.

[0074] In accordance with another aspect of the invention, a distractoris inserted into the disc space in one of the previously trephineopenings. In a similar manner, a second distractor is inserted into thesecond trephined opening. If necessary, a distractor having two workingheights is inserted in a first smaller height and rotated 90 degreesafter insertion to a second larger height. Moreover, a tip having thedesired configuration may be selected and mounted on the modulardistraction assembly 150 prior to insertion. In some instances, the tipmay be disconnected from the distractor assembly and temporarily left inthe disc space.

[0075] The further description of the method will be described withrespect to placement of single dowel, it being understood that the stepsmay be repeated on the opposite side to implant a second implant. Aguide tube is positioned over the distractor and advanced until thedistracting flanges are positioned in the disc space. It will beunderstood that the enlarged portion on the distractor shaft guides theguide tube into a concentric position about the distractor. Once theguide tube is securely seated, the distractor may be withdrawn. The discspace will then be prepared to receive an implant having a preselectedlength and diameter. A reamer of the appropriate diameter is selectedand a depth stop according to the present invention is positioned on theshaft at the preselected depth markings. The reamer is rotatablyadvanced into the disc space until the depth stop engages the guide tubeto limit further advancement. Preferably, a depth gauge according to thepresent invention is inserted to verify complete reaming to thepreselected depth and removal of debris. If a threaded implant will beused, a depth stop will be positioned on a tap shaft at the preselecteddepth. The tap is rotatably inserted into the disc space until the depthstop engages the guide tube. The tap is removed and the depth gauge maybe reinserted to verify that the proper sized opening has been formedand is substantially unobstructed. At this point an implant is insertedusing the implant inserter. Once the implant is inserted, the guide tubemay be withdrawn and the procedure repeated on the opposite side.

[0076] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiments have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A retractor, comprising: a retractor blade; ashaft having a first portion and an opposite second portion, said firstportion connected to said retractor blade; a handle pivotally mounted onsaid second portion; and a locking mechanism selectively locking saidhandle to said second portion to limit pivotal movement of said handlein relation to said shaft.
 2. The retractor of claim 1 , wherein saidlocking mechanism includes said second end having a plurality of groovesand said handle includes a projecting portion selectively engageablewith at least one of said grooves.
 3. The retractor of claim 1 , whereinsaid handle is removably mounted on said second portion.
 4. Theretractor of claim 1 , wherein said locking mechanism locks into aplurality of preset positions.
 5. The retractor of claim 4 , whereinsaid locking mechanism includes at least four preset positions.
 6. Theretractor of claim 4 , wherein said locking mechanism includes eightpreset positions.
 7. The retractor of claim 1 , wherein said shaftincludes a first longitudinal axis and said handle includes a secondlongitudinal axis, said second axis intersecting said first axis atapproximately a 45 degree angle.
 8. The retractor of claim 2 , whereinsaid includes a mechanism to biase the locking mechanism to a lockedposition.
 9. The retractor of claim 3 , wherein said handle includes achamber for receiving said second portion, said chamber having anopening for passage of said second portion and a locking arm moveablebetween a locked position, an adjustment position, and a releasedposition, said locked position limiting pivotal movement of said handlein relation to said shaft, said adjustment position permitting pivotalmovement of said handle in relation to said shaft but preventing removalof said handle from said shaft, and said released position permittingremoval of said handle from said shaft.
 10. A method of dura retractionfor posterior access in the spine, the method comprising: providing aretractor having a retractor blade pivotally connected to a handle witha locking mechanism to selectively lock the handle to the retractor;exposing a portion of the dura; inserting the retractor with the handlein an insertion position and the locking mechanism in a locked position;retracting the dura to expose underlying spinal elements; unlocking thelocking mechanism to allow the handle to pivot in relation to theretractor blade; pivoting the handle to a holding position; and lockingthe locking mechanism to maintain the handle in the locked position. 11.A template for straddling the dura in a spinal surgery to facilitatemarking a surgical site, said template comprising: a body portion havingan upper surface and a lower surface, and an opening formed between saidupper surface and said lower surface; a shaft having a first end and asecond end, said first end connected to said upper surface; a workingtube positioned in substantial alignment with said opening and extendingfrom said lower surface, said tube having a first diameter; and alocator extension engaged with said body, said locator extensionextending from said lower surface and spaced from said working tube toprovide a space for the dura, said locator extension have a seconddiameter that is less than said first diameter.
 12. The template ofclaim 11 , wherein said locator extension is removably engaged with saidbody.
 13. The template of claim 11 , wherein said body is sized toapproximate a maximum area of an instrument set, and said body includesa perimeter with a plurality of notches for marking tissue that must beremoved to accommodate the instrument set.
 14. The template of claim 11, further including a handle pivotally connected to said second end anda locking mechanism controllable to selectively limit pivotal movementbetween said shaft and said handle.
 15. The template of claim 11 ,wherein said locator extension is solid.
 16. The template of claim 11 ,wherein said working tube is integral with said body.
 17. The templateof claim 11 , wherein said locator extension includes a connection endconnected to said body, an opposite engagement end and a curved portionbetween said connection end and said engagement end.
 18. The template ofclaim 11 , wherein said shaft includes an offset segment between saidfirst end and said second end.
 19. The template of claim 13 , whereinsaid body includes two inter-connected semi-circular lobes defining themaximum area of an instrument set.
 20. A spinal disc space distractorassembly, the assembly comprising: an outer shaft having a first end andan opposite second end, said shaft including a first driving shoulderadjacent said first end for transmitting rotational force and anopposite second driving shoulder adjacent said second end for receivinga rotational force; an inner shaft slidably disposed within at least aportion of said outer shaft, said inner shaft having a first connectionend and an opposite second connection end, said first connection enddisposed adjacent said first end; a distraction tip, said tip having adriving surface adapted for engagement with said first driving shoulderand a connection surface adapted for engagement with said firstconnection end; and a handle having a connection mechanism selectivelyengagable with said second connection end and a handle driving surfaceadapted for engagement with said second driving shoulder to transmitrotational force; wherein with said inner shaft connected to said tip,connection of said connection mechanism with said inner shaft secondconnection end maintains said first driving end in engagement with saiddriving surface and said second driving end in engagement with saidsecond driving surface.
 21. The distractor of claim 20 , wherein saidouter shaft includes a tapered portion between said first end and saidsecond end.
 22. The distractor of claim 21 , wherein said first end hasa smaller diameter than said second end.
 23. The distractor of claim 20, wherein said outer shaft includes a longitudinal axis and defines awindow extending through said shaft transverse to said longitudinalaxis.
 24. The distractor of claim 20 , wherein said inner shaft iscaptured within said outer shaft to limit movement between said outershaft and said inner shaft.
 25. A spinal disc space distractor,comprising: a distractor tip; and a shaft having a first end connectedto said distractor tip, an opposite second end and a tapering portiondisposed between said first end and said second end, said taperingportion tapering from a larger configuration proximal said second end toa smaller configuration proximal said first end.
 26. The distractor ofclaim 25 , wherein said shaft includes a longitudinal axis and defines awindow extending through said shaft transverse to said longitudinalaxis.
 27. The distractor of claim 25 , wherein said distractor tip isremovably connected to said shaft.
 28. The distractor of claim 27 ,further including an inner shaft disposed within said outer shaft, saidinner shaft adapted to engage said distractor tip.
 29. A spinal discspace distractor, comprising: a shaft having a first end and an oppositesecond end with a longitudinal axis extending between said first end andsaid second end; a distractor tip disposed adjacent said first end; andsaid shaft defining a window extending transverse to said longitudinalaxis.
 30. An instrument for determining correct formation of an openingbetween two adjacent vertebra, said instrument comprising: a shaft; aprobe having the dimensions of an opening to receiving an implant, saidprobe attached to said shaft.
 31. An instrument for evaluating the depthof an opening between two adjacent vertebral bodies, comprising: anelongated shaft; a radiolucent tip attached to said shaft, said tipincluding at least on radiopaque marker.